Posts Tagged ‘ heated build platform

Building the C-Bot 3d Printer : Part 33 : Machining a mic6 aluminum removable build plate

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Overview

I’ve been using removable glass build plates for years on both my Makerbot Replicator 1, and my custom C-Bot:  I get double-thick glass cut at my local hardware store (Orchard Supply Hardware has had a great price on this), always thinking it was ‘totally flat’.  But is it really?  My C-Bot has a 12×12″ heated build platform.  When I go to level it with the glass, I get each of the four corners dialed in perfectly.  But the middle always sags slightly… even though it’s glass.  Double-thick glass.  But glass is actually somewhat plastic, and this sag has always bugged me.

Back in December I assembled my 1000mm X-Carve CNC, and it’s been so much fun cutting wood.  I knew it could do aluminum as well, but needed  a project.  And that’s what this post is all about:  Using my X-Carve to machine a new removable build plate out of .25″ mic6 aluminum for my 3d printer.  I am so happy with the results.

Sourcing the material

Before I started this, I had no idea what ‘mic6’ aluminum was.  It’s also referred to as ‘cast aluminum tooling plate’ or ‘ATP’, since mic6 appears to be a trademarked brand name.  Simplistically, it’s a standard for (among other things) a very flat aluminum plate, to .001″.  After reading a plethora of forms, and researching my local options, I settled on Midwest Steel And Aluminum’s “Cast Aluminum Tool & Jig Plate“, .25″ thick, 12×12”, which came to about $20, and the ground shipping another $20.  I could have bought it locally for $45 + tax (ugh).

A note on the order:  The plate was packaged in one layer of cardboard, that was it.  It appeared to have been dropped several times in-transit, 3 of the 4 corners were blunted, and there was an small indentation in the middle of plate itself.  If I was using this for something really precision I would have returned it.  Just a note to tell them to ship it better if you go this route.

Once it showed up, time to make some cuts!

Initial cuts

When I first got the plate I knew I had to notch a section out of each corner, since the heads of the bolts that hold the MakerFarm heated build platform stick up about 1/8″ish from it:  I didn’t want the plate resting on the bolt-heads, so I need to make little pockets for each.  Before I even considered my X-Carve CNC, I figured I could use my drill-press to pocket these.  Long story short:  It did not work well, and made a mess of the corners.  Based on that frustration I went down the ‘how about I use that dormant CNC right next to the drill press…” road.

For all below cuts, I used the same 1/8″ 2-flue upcut carbide endmill.

Since these cuts were so simple, I used Inventable’s Easel: I designed a circle with a diameter of .4″ across, .175″ deep, and used that to pocket each of the four corners already mangled by my drill press.  I used the default ‘aluminum’ Easel setting (5 ipm, .003″ doc, DeWalt on speed 1) with the first pocket (which took about 20 minutes), then started cranking it up: By the final pocket I had it running at 20 ipm at .01″ doc, with the DeWalt on speed 2, taking about 5 minutes..  It did great, and the bit was cool to the touch after the cuts.  When all four pockets were complete, it fit right on the bed with no collision with the bolt-heads:

cornerPocketAll the rough stuff to the right of the bolt-head was the abuse by the drill-press.

I have four bulldog clips that hold the plate on, one on the middle of each side.  The issue is even though I’ve bent them down to move them out of the way, parts of them still stick up slightly, and on a large print the nozzle could collide with them.  So going back to Easel, I designed a new rectangular pocket that would keep the bulldogs out of the way of the toolhead.  These were 2.25″ x .3″, cut .075″ deep.  I positioned them in the center of the left\right sides of the build plate, but had to offset them on the front\back based on my leadscrew config.

An in-process cut:

bottomPocketCut

And all four final cuts:

bottomPockets

Installed on the printer:  No more clearance problems with the bulldogs! :)

topBulldog

Prepping the plate

I use a highly secret (50% wood-glue, 50% water) slurry on my build plate to get PLA to stick.  But the mic6 is so smooth, I first scoured it with steel wool for several minutes to give the glue something to bite into.

Note for the future:  First, use something like lacquer thinner\acetone\mineral spirits to clean the plate of any oils:  Quite to my surprise, after many minutes of scrubbing, I could clearly see my handprint on it.  The oils deposited from my hand actually protected it from the steel wool.  So I went back and liberally scrubbed it with lacquer-thinner soaked rag, then went back to the steel-wool treatment again:  No more handprint.  Be sure to wipe it down with lacquer thinner after the steel wool too:  The wool actually leaves quite a bit of itself deposited into the aluminum.

After the plate was scrubbed, cleaned, and glue-slurry applied, I did some test prints.  And while the flatness was super awesome, I realized something very quickly:  The slicer said the bed heated up waaaay faster than it actually did:  For big prints in PLA, I’ll heat the bed up to 60c.

It dawned on me that the thermistor that does the temp reading is taped to the bottom of the MakerFarm heated build platform, while the thing being printed is sitting above it on .25″ of aluminum… that is taking much longer to heat up.

After brainstorming, I came up with the idea of cutting a groove into the bottom of the plate, that I could tape the thermistor into:  It should then be reading the temp from the removable plate itself, providing a much more accurate temperature.  This means I’ll also need to snip the leads running to the thermistor and install a barrel-jack into the mix to allow for the plate to be removed, since there’s now a sensor taped to it.

Secondary cut

Going back to Easel, I designed a .5″ wide groove cut .0312″ deep that I could recess the tape into, then another smaller groove .2″ across and .1″ deep to run the wires to the thermistor.

Here it is mid-cut:

bottomGrooveCut

Cut gotchas:

  • Easel has (based on what I’ve experienced) no idea of conventional cuts (bit spinning in the direction of travel) and climb cuts (bit spinning opposite direction of travel).  From what I’ve read, climb cuts can provide better finish, but only on ‘professional\beefy’ machines:  not the X-Carve.  Conventional cuts fare much better on the X-Carve.  This (as I found out) can cause dangerous problems.
  • When the top cut started, it was all conventional cuts, and cut fine.  But when the next layer started, and for every layer down, it was climb cuts.  Because of that, I noticed a lot of bit defection, chattering, and even gouging.  To avoid catastrophe, I had to manually monitor the cut, and really crank up the spindle speed as needed to compensate.
  • Note that MeshCAM gives you the option in the rough-cut to do either conventional or climb cut:  For future aluminum projects I’ll be using it for sure.

To help with heat transfer (that is only a theory of mine) and to prevent any sort of plate-slip (which is legit), I shoot the bottom of the plate with rubberized undercoating.  I then snipped my thermistor line, soldered barrel-jacks onto either side of it, then taped it into the groove on the bottom of the plate:

bottomFinal

Putting it back onto the HPB, I reconnected the barrel-jacks:

underWiring

Final thoughts

It works, great.

topFinal

When the HPB heats up, and it finally gets to temp…. it really feels like the top\bottom are the same temp.  And I can level each of the four corners, and the middle is the exact same distance as the rest of them from the toolhead.

Super rewarding project with one machine improving another.


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Repairing The Replicators HBP Cable

About nine months ago, I blogged about how the cable to my Makerbot Replicator’s heated build platform (hbp) fried.  Their support was really responsive and shipped me out a new cable that fixed the problem.  Well, it fried again.  And if something breaks twice, I start to think about how I can make it ‘better’.

Took me a while to understand what went wrong, since from the top it looked just fine:

But after removal, the problem was plainly visible:

After checking the forums, there were several suggestions from knowledgeable users to make a separate connection for the main positive and negative leads, using 14-16 gauge cable.  When I went to the local electronics store, I could only find connectors in 18 gauge, or 12.  I went with 12.  Which is huuuuge for this, but hey, sometimes you have to work with what you have 😉

The first step was to use a Dremel cutting wheel to hack off the positive & negative connectors:

Since the connector I purchased wasn’t long enough to reach the Mightyboard, I had to solder on some (slightly smaller) extensions.  This also shows off the actual connector point itself:  This allows me to disconnect the whole hbp from the Mightyboard, for future removal if needed.  This section sits directly under the hbp itself (when final cable routing is performed).

I ended up wrapping the whole thing in heat-shrink tubing.

The next tricky bit was soldering the 12-gauge wires to the hbp itself.  To make room, I bent the left-most lead over.  And to keep all the twisted strands from shooting all over the place, I tied a noose around each using the wire from a twist-tie:

Next came the soldering:

After which I removed the nooses.  Finally I wrapped them up in electrical tape, and reconnected everything on both ends of the cables (no pic of the Mightyboard connection, but it’s pretty much the same as before, just with two bigger cables running into it):

I was a little scared to fire it up and start heating the platform, but it performed flawlessly.  And with the larger gauge cables, heats up faster too.  If things are still working nine months from now, I guess the fix worked 😉

 

New Removable Build Platform: Glass

In a previous post, I describe how I made a removable build platform for my Makerbot Replicator (1) using a sheet of Lexan.  This was a huge improvement to the printer, since by default the Replicator doesn’t have a removable platform, and getting large prints off the stock platform could create a lot of torquing on the platform and arms, causing constant recalibration.  Plus over time, I presume this would damage the machine.

The Lexan platform has been working great.  However, I did run into one problem:  Large prints would actually warp the platform as they stuck to it, creating prints that weren’t perfectly flat.  If you’re making single part prints, I have yet to find this to be an issue.  But I was working on a project (hopefully I’ll be able to show it in a future post) that required eight separate prints, all combined together interlocking with pegs.  Very quickly I realized that even though the prints were sticking to the Lexan, they were actually warping the lexan and when removed, weren’t perfectly flat.

Enter glass:  I went to a local craft store’s (Michaels) framing department, and had them cut two pieces of glass to the size of the platform, for about $12 each.  At home, I used my Dremel and a grinding stone to round off the sharp corners.  I’d read that you can use hair-spray to create an adhesion layer on the glass, and picked up some “Unscented Aquanet Extra Super Hold” for a few bucks.  Applying two layers (letting the first layer dry) worked great:  The test prints I did worked flawlessly, along with many future prints.  I also found that putting blue-painters tape directly on the glass works very well.  In addition, heating the platform seemed to transfer directly to the glass, helping to reduce additional warpage.

The best part?  Large prints that are really stuck on there will just pop off after a few seconds being left in the freezer.

Lexan: The 3D-printer build platform of the future

Before we get started, here’s the end result:

Now let’s go back in time….

Being a Makerbot Replicator (1) owner, I don’t have a removable print platform:  The results are printed directly onto the HBP (Heated Build Platform), from which you have to remove them upon completion.  If it is a large print, and stuck on there really good, it can totally screw up your leveling\calibration for the next print, based on all the torquing that you inflict upon the platform getting the print off.  Furthermore, if you print in ABS, there’s a good chance you’ll somehow mangle the Kapton tape stuck to the HBP, or printing with PLA, rip up your blue painters tape.

While browsing the Makerbot Operators Google Group, I read about people using glass as a cover for the HBP:  Not only does it give you a completely level surface, but by putting down a layer of hairspray on it, your parts can stick to it as well.  I was about to go out and and get some glass cut, when I ran across another thread  talking about Lexan (a polycarbonate) being used as a build surface (that guy is selling it pre-cut for the Replicator 2, but since I’m Rep1, I’m out of luck and have to come up with my own solution).  Plugging that keyword into the Googles, I found many other people had used Lexan successfully, so I thought I’d give it a shot:  I liked the idea of something that couldn’t crack and slice my hand open under stress as my print bed.  All that being said, I read many arguments for the pro’s and con’s of each (glass, Lexan, acrylic, etc).  This post is mainly about the pro’s I’ve encountered with Lexan (no con’s yet).

Went to Home Depot, and picked up an overside sheet since I’d never worked with the material before:  Wanted to make sure I could do some test cuts before I did the real thing.  Here’s an example of what I purchased.

It turned out to be really easy to slice up on my table saw.  Armed with some binder-clips, I had it mounted to my Replicator in no time.  But then the first problem dawned on me:  the platform is now 2.35mm higher than before.  How can I compensate for this height adjustment?  The adjustment screws weren’t giving me enough play.  Querying the forums, I found out you can actually adjust the z-axis switch location.  On my bot, it is mounted in fixed holes on the back wall.  But unscrewing it, you can move it over to a variable position system (which I’d never noticed before) which sovles this problem:  I moved it down the desired amount, re-leveled the whole platform, and thought I was in business.

Then the second problem appeared:  After clipping it to the build platform, the Lexan was warping.  As it turns out, the bolts that hold the HBP together actually stick up a small amount above the platform.  I’d noticed this before when applying the tape, but since it’s on the extremities, never thought much of it.  But when the clips press down on the lexan, they flex around those bolt-heads causing for an uneven surface.  I took a close-up shot of the problem:

In the above image, you can see the calibration bolt, and you can see how to the right, the lexan has risen slightly above the build surface.  This made for some really bad initial printing tests.

I got the thought in my head to mill out the area around each bolt-head using my drill press:  I used a black sharpie to mark the position of each bolt-head on the lexan, and drilled out a few mm if the Lexan at each spot:

I should note that it’s important to have your lexan on some other hard flat surface when drilling:  My drill press has an open-space on the platform below the drill bit (normally you want that so you don’t drill straight into the platform’s steel bed).  But I found that the area beneath the carved-out zone would bulge under the drills weight\heat\pressure, which is obviously no-good.  Putting another piece of lexan under the first, and drilling very slowly solved this bulging issue completely.

Clipping that back to the HBP gave great results:

The Lexan mounts completely flat to the HBP now.  When I level it with my awesome calibration tool, I can get it within .01mm across the whole platform.

The final print results are great:  PLA sticks to the Lexan super good.  For smaller items (yet to print anything ‘big’), I need use my razor blade scraper to get them off.  And for bigger prints, since the Lexan is flexible, they should be much easier to bend and ‘pop’ off.  And of course, the whole thing is just held on with binder-clips, which means in theory I won’t need to keep re-leveling my platform after a tough print fails to release.  Plus I can cut back on my blue-tape usage…

So here are some shots of the end result.  Overall, extremely happy with the results.